Add TryGetOwnedMemory (dotnet/coreclr#16455)

* Add TryGetOwnedMemory

* Feedback

* spelling

Signed-off-by: dotnet-bot-corefx-mirror <dotnet-bot@microsoft.com>

Author: benaadams

src/Common/src/CoreLib/System/Runtime/InteropServices/MemoryMarshal.cs

@@ -39,6 +39,30 @@ public static bool TryGetArray<T>(ReadOnlyMemory<T> readOnlyMemory, out ArraySeg
             return false;
         }
 
+        /// <summary>
+        /// Get a <see cref="OwnedMemory{T}"/> from the underlying memory.
+        /// If unable to get the <typeparamref name="TOwner"/>, return false with a default <typeparamref name="TOwner"/>.
+        /// </summary>
+        public static bool TryGetOwnedMemory<T, TOwner>(ReadOnlyMemory<T> readOnlyMemory, out TOwner ownedMemory)
+            where TOwner : OwnedMemory<T>
+        {
+            TOwner owner; // Use register for null comparison rather than byref
+            ownedMemory = owner = readOnlyMemory.GetObjectStartLength(out int index, out int length) as TOwner;
+            return !ReferenceEquals(owner, null);
+        }
+
+        /// <summary>
+        /// Get a <see cref="OwnedMemory{T}"/> and <param name="index">, <param name="length"> on the <see cref="OwnedMemory{T}"/> from the underlying memory.
+        /// If unable to get the <typeparamref name="TOwner"/>, return false with a default <typeparamref name="TOwner"/>.
+        /// </summary>
+        public static bool TryGetOwnedMemory<T, TOwner>(ReadOnlyMemory<T> readOnlyMemory, out TOwner ownedMemory, out int index, out int length)
+           where TOwner : OwnedMemory<T>
+        {
+            TOwner owner; // Use register for null comparison rather than byref
+            ownedMemory = owner = readOnlyMemory.GetObjectStartLength(out index, out length) as TOwner;
+            return !ReferenceEquals(owner, null);
+        }
+
         /// <summary>
         /// Creates an <see cref="IEnumerable{T}"/> view of the given <paramref name="memory" /> to allow
         /// the <paramref name="memory" /> to be used in existing APIs that take an <see cref="IEnumerable{T}"/>.